A plastic material is any of a wide range of synthetic, semi-synthetic, or natural organic solids that may be moldable. Plastics are typically organic polymers of high molecular mass, but they often contain other substances. Early plastics were bio-derived materials such as egg and blood proteins, which are organic polymers. In the 1800s, the development of plastics accelerated with Charles Goodyear's discovery of vulcanization as a route to thermoset materials derived from natural rubber. After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new polymers were polystyrene (PS) and polyvinyl chloride (PVC). The development of plastics has come from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., rubber, nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, PVC). Plastics are durable and degrade slowly because the chemical bonds that make plastic so durable, make it equally resistant to natural processes of degradation. As a result, most plastic we use today will either be incinerated or end up in a landfill for many years.